1. Field of the Invention
Embodiments of the present invention relate to a thin film transistor, a method of fabricating the same, and an organic light emitting diode display device including the same. More particularly, embodiments of the present invention relate to a thin film transistor (TFT) that can prevent generated Joule heat from generating an arc during a conventional crystallization process.
2. Description of the Related Art
Annealing methods used during a crystallization process generally include a furnace annealing method using a heat furnace, a rapid thermal annealing (RTA) method using radiant heat, e.g., a halogen lamp, a laser annealing method using a laser, and an annealing method using Joule heating. Among available annealing methods, an appropriate annealing method for the crystallization process is determined based on characteristics of material and process contemplated. Some of the factors to be considered in the selection of an appropriate annealing method are a range of an annealing temperature, uniformity of the annealing temperature, a heating rate, a cooling rate, purchase price, and maintenance cost. However, a selection of annealing method becomes very limited when high temperature annealing or high rate annealing only in a local region of a material is needed.
The laser annealing method can rapidly anneal a surface of a material. Despite this advantage, the laser annealing method has only limited applicability, since it can only be used to anneal particular materials. When scanned linear laser beams overlap to anneal a large-sized device, non-uniformity in intensity of the laser beam and in irradiation level of the laser beam may occur. Also, the laser annealing method requires very expensive equipment, as well as incurring high maintenance cost.
The RTA method is widely applied to a semiconductor fabrication process. However, with current technology, RTA methods can be applied only to a 300 mm silicon wafer, so it is difficult to uniformly anneal a substrate larger than 300 mm. Moreover, this method has a maximum heating rate of about 400° C./sec, and thus cannot be applied to a process requiring a higher heating rate than 400° C./sec.
Thus, research has been widely conducted on annealing methods to solve these problems and to eliminate processing limitations. A rapid annealing method, which applies an electrical field to a conductive layer and generates Joule heat, can rapidly anneal a selected material by transferring high heat. The rapid annealing method has much higher heating rate than that of the conventional RTA method. However, such a rapid annealing method cannot prevent physical defects of substrates from an arc generated during the Joule heating.